1. Field of the Invention
The present invention relates to a cornea shape measuring apparatus capable of measuring an eye's refractive index and a shape of the cornea of the subject's eye.
2. Description of the Prior Art
As a cornea shape measuring apparatus for measuring a cornea shape precisely, there has been heretofore known a cornea shape measuring apparatus comprising a planar and circular pattern plate, a concentric circle shape light transparent portion, namely, a transparent ring-shaped pattern (a placido pattern) provided on the pattern plate, and a light source disposed behind the pattern plate, the light emitted from the light source being formed into light flux of a number of concentric circle shape ring-shaped patterns through the transparent ring-shaped pattern, the light flux of the concentric circle shape ring-shaped patterns being projected toward the cornea of the subject's eye, to what degree the concentric circle shape transparent pattern changes as compared with the projected pattern shape being recognized so that the shape of the cornea is judged from the obtained change in shape.
In such a cornea shape measuring apparatus as described above, in case of obtaining the cornea shape accurately, it is suggested that the number of concentric circle shape transparent ring-shaped patterns be as many as possible. However, if an attempt is made to increase the number of transparent ring-shaped patterns, the outermost pattern out of the ring-shaped patterns provided on the pattern plate is enlarged in its diameter, thus the entire apparatus being large-sized. Thus there is a limit in increasing the number of transparent ring-shaped patterns.
Further, where an attempt is made to increase the number of transparent ring-shaped patterns, there arises a problem in that since the pattern plate is away from the subject's eye, a large quantity of light is necessary for the light source. Particularly, outer one of the transparent ring-shaped patterns of the pattern plate is away from the subject's eye, hence the quantity of light projected from the outer transparent ring-shaped pattern lowers. Therefore, in order that the quantity of light of the ring-shaped patterns projected on the subject's eye from a number of transparent ring-shaped patterns is made substantially uniform, it is necessary to make the quantity of light from the outer transparent ring-shaped patterns larger.
It is therefore an object of the present invention to provide a cornea shape measuring apparatus capable of increasing the number of transparent ring-shaped patterns, without making the entire apparatus large-sized, to project the ring-shaped patterns over a wide range of the cornea of the subject's eye, and obtaining a sufficient quantity of illuminating light with the minimum light source.